This project is designed to study the thermal energy flow in the rock environment built of granitic rocks, both in terms of efficiency as well as safety. In the frame of an in-situ experiment a study of heat stress of rock is carried out in underground laboratory Josef (central Europe). Relative stress changes in granitic rock environment induced by cyclic thermal loading at c. 120 m depth are being continuously monitored in order to evaluate the influence of the thermal load increments. The rock massif is monitored in c. 10m perimeter around a heating borehole, being built by faulted/fractured granitic rocks crosscut by a swarm of quartz veinlets. The main objective of the laboratory and field experiments and related studies is to confirm or eliminate any possible changes in physical and chemical parameters of granitic rocks exposed to thermal load of maximum 95&$176;C. Appropriate attention is also paid to variations in the flow and circulation of groundwater and to the deformation of the rock massif caused by heating – cooling cycles. These are the key parameters necessary for the safe design and construction of underground facilities proposed for the storage of thermal energy or for waste disposal of materials that produce heat (e.g. nuclear waste).
Geotechnical monitoring is focused on stress and strain changes in rock matrix (stressmeters and strain gages), pore pressure (piezometers) and displacements induced along fractures (micro and 3D crackmeters). Present results indicate very rapid reaction of the rock massif to fluctuations in rock heating intensity and large extent of these artificially induced stress changes. The changes appear without any observable hysteresis, i.e. they behave as fully reversible in respect to irregular experimental heat supply modifications.
The influence of infilling material on rock samples often becomes a problem in determining the shear strength. In fact, discontinuity such as joint is often encountered in rock mass. The presence of discontinuity will change the behavior of rock mass. This phenomena become worst when the joint filled by infilling material. There many problems in the design and construction due to the presence of filled joint rock Concerning with the signification the effect of filled joint to its shear strength it is necessary to carry out tests on rock samples. A series of laboratory experimentation is carried out to model the filled joint by using Tuff as a joint block and clay infilling material. In these tests is varying parameters of normal stress, infilling thickness and roughness of joint surface. From the test it is showed that the shear strength of a joint decreased significantly with the presence of infilling material in the aperture of a joint. The effect of asperities has influence 25-50% in shear strength of the thickness of the asperities. In tropical country as Indonesia, it is evident that asperities influence of Tuff on the shear strength in tropical country higher than non tropical country, the reduction of shear strength depends on the thickness of infilling material are cohesion of sample filled 0.25 cm of thickness and sample filled 0.5 cm of thickness decrease 73.63% and 86.91% of natural sample condition.
To examine the features of fractures induced by hydraulic fracturing and the surrounding stimulated regions, a hydraulic fracturing experiment was conducted using shale samples. In this experiment, the fracturing fluid was a thermosetting resin, methyl metaacrylate (MMA), mixed with a fluorescent paint, and just after fracturing the resin was immediately fixed within the sample by heating. Cut sections of the samples were observed under ultraviolet light irradiation. It is expected that the hydraulically induced fractures and the surrounding fractured region will be detected because the induced fractures filled with resin should emit light, while the other parts will not.
The samples, which were collected from the Kushiro Coal Mine in Hokkaido, Japan at the depth around275m,were roughly 85mm in diameter,170mm in length, and cored normal to the sedimentary planes. An injection hole with a10-mm diameter was drilled onto the center of the sample parallel to the sedimentary plane to simulate hydraulic fracturing in shale gas development. The experiment was conducted under a uniaxial loading condition of 3MPa and the fracturing fluid was injected into the sealed injection hole at a constant flow rate.
The main fracture induced by hydraulic fracturing, which was subsequently filled and fixed with the resin, is clearly observed. Detailed microscopic observations show that the main fracture is accompanied by many thinner secondary branches. Furthermore, fractured regions around the induced main fracture, which penetrate with the resin and emitted light under ultraviolet light irradiation, are also observed. It is confirmed that the region influenced by hydraulic fracturing around the main fractures exists. This fractured region is considered to be the stimulated region where the permeability is improved, presumably because the main fracture forms a new fracture network and/or activates a pre-existing one.
During this brief temporal window, a secondary fracture can be created in a completely different direction, resulting in much higher probability of maximized well production. Such methods warrant the availability of data related to the dynamic behavior of rocks. Such data includes rock compression, slip data between rock layers, and the amount of energy stored within such slip planes, all recorded as a function of time. To offer this capability, a new testing device was designed specifically for this purpose. The test fixture accepts three layers of rocks, which could be the same or different type rocks (depending on requirements), which are then stressed and pressurized gradually to represent the real stresses and pore pressures inside a formation. Rock compression to mimic a fracture stimulation treatment is simulated by pressurizing one side of one of the rock layers. Accurate linear displacement sensors are used to sense rock layer motion; hence, compression and slip data can be recorded. Additionally, the device also records micro-seismic signals, which are accurately triangulated to locate the tip of the slip, to further characterize the unique behavior of the rock during stimulation.
Inoue, N. (Pontifical Catholic University of Rio de Janeiro) | da Fontoura, S. A. B. (Pontifical Catholic University of Rio de Janeiro) | Righetto, G. L. (Pontifical Catholic University of Rio de Janeiro) | Lautenschlager, C. E. R. (Pontifical Catholic University of Rio de Janeiro) | Albuquerque, R. A. do C. (Pontifical Catholic University of Rio de Janeiro) | Meurer, G. B. (Petrobras, Rio de Janeiro) | de Souza, A. L. S. (Petrobras, Rio de Janeiro)
A Reservoir Geomechanics Workflow has been developed in order to evaluate the geomechanical effects caused by reservoir production in a fast, easy and accurate way. Whole reservoir geomechanics workflow is carried out inside a GOCAD environment that is comprised of three steps: the pre-processing (data set preparation); the running of the coupling program (coupled analysis) and; post-processing (results visualization). However, for practical purposes, a real reservoir simulation that takes account of the so-called geomechanical effects was carried out after solving three issues: finite element mesh construction; hydro-mechanical coupling and; processing time. The discretization of a finite element mesh of the reservoir and surrounding rocks is not trivial task using a conventional finite element pre-processor. Thus, a customized plug-in was implemented for the generation of finite element mesh in the program GOCAD (used in geological modeling). A reliable/robust partial coupling scheme was developed and implemented between a conventional reservoir simulator and a finite element program. The processing time spent on stress analysis (finite element program) was reduced through implementation of an in-house parallel finite element program that was written on GPU (Graphics Processing Unit).
Jiang, Yujing (Nagasaki University) | Wang, Xiaoshan (Nagasaki University) | Li, Bo (Nagasaki University) | Higashi, Yukihiro (Geoscience Research Laboratory Co. Ltd) | Taniguchi, Kenshi (Nippon Steel & Sumikin Materials Co. Ltd) | Koga, Dairoku (Eight-Japan Engineering Consultants Inc.) | Ishida, Kosei (Reliable Materials & Technology)
Extensive experimental verifications have shown that the existing reinforced concrete (RC) members can be strengthened with externally bonded FRP composites. However, until now, the construction cases of applying the FRP-PCM method to tunnel lining are still few, and the design routine of this method based on the quantitative evaluation of reinforcement effects has not been established. Numerical simulations of tunnel deformation caused by loosening pressure were conducted. Reinforcement effects using the FRP-PCM method in the cases with different rock mass rating, loosening height and deterioration level of lining concrete were also discussed. Keywords: Tunnel lining, Polymer Cement Modified (PCM), Fiber Reinforcement Plastics (FRP), Cavity, Loosening pressure, Reinforcement effect 1. Introduction In recent years, many tunnels that have been commissioned for several decades have suffered damages in different degrees, especially on lining concrete.
Guo, Liang (Nanjing University) | Li, Xiao-zhao (NJU-ECE Institute for Underground and Geo-environment) | Zhou, Yang-yi (Nanjing University) | Zhang, Yang-song (NJU-ECE Institute for Underground and Geo-environment) | Suo, Pei-si (Nanjing University)
The accuracy of seepage calculations in rock mass is directly influenced by the confidence level of the corresponding discontinuities network models. For the purpose of more efficient application of the stochastic discontinuities model, improvements of efficiency, both in-situ measurements and subsequent statistical analyses with respect to the discontinuities parameters are needed. New digital techniques, e.g. GPS (Global Positioning System) and GIS (Geographical Information System), are applied to the in-situ measurements and data processing of discontinuities parameters. Confidence level of the new model is significantly augmented compared with the accuracy and sampling quantity of the less efficient and more labor-intensive traditional in-situ measurements. Over 10,000 discontinuities were measured using GPS in Chinese high-level radioactive waste repository candidate site in Beishan. The three-dimensional stochastic discontinuities network model is established based upon the statistical analyses of the digitalized samples. The accuracy of the model is graphically and numerically validated. Results suggest that higher accuracy of the stochastic model is obtained based on the proposed digital techniques, and the requirement of engineering application is better fulfilled.
In recent years, the frequency of heavy rain is increasing in Japan. Even if it is a stable slope until now, many of slopes will become unstable by the increase in heavy rain in the future. In some cases of landslides in the reservoir area near the dam, the hydraulic bore is caused by slope failure in the reservoir, As a result, there is a risk that hydroelectric facilities may be damaged. In addition, the development of sedimentation of the reservoir by landslides is concerned. In this paper, evaluation of the landslide risk of slope in the dam reservoir area is described taking into account the seepage of rainfall into the slope of drainage basin. The slope stability is evaluated, using the digital elevation model (=DEM) of entire drainage basin and its infiltration into the slope. In particular, we analyzed the effect of mesh size of DEM for the evaluation.
As a safety assessment of the geological disposal of high-level radioactive wastes deep in a rock mass, it is important to grasp the characteristic of permeability and mass transport. If the rock mass around a disposal site is crystalline material, joints can be involved in the rock mass. Since the cubic law of joint opening displacement is often used to evaluate flow properties briefly, it is necessary to discuss the applicability of the cubic law for the evaluation of flow properties. However, the complex-ity of joint form brings about the difficulty for the discussion of the applicability by an empirical method. Thus, in this study, a numerical approach is used for the discussion. As a method of numeri-cal approach, Lattice Boltzmann Method in which hydraulic gradient can be given as boundary condi-tions is employed. The influence of joint form on the flow property is examined through the Lattice Boltzmann analysis. In the result, it is clarified that the evaluation by the cubic law of joint opening displacement is valid from safety point of view although the hydraulic conductivity evaluated by the cubic law is slightly different from the numerical one. Furthermore, the flow through a joint is analyzed so as to reproduce the experimental flow test in which the distributions of opening displacement and geological form of the joint are grasped, and the analysis result is compared with measured one. In the result, the flow rate obtained from the LBM analysis is more closely to the measured one than that evaluated by the cubic law. Thus, it is founded that the evaluation of the flow through the joint involved in a rock mass by Lattice Boltzmann Method is more effective than the cube law.
Suzuki, Kazuki (Tokyo Metropolitan University) | Domon, Tsuyoshi (Tokyo Metropolitan University) | Nishimura, Kazuo (Tokyo Metropolitan University) | Kitamura, Hazime (Nippon Expressway Research Institute Co., Ltd.) | Yasui, Shigetoyo (Japan Construction Method and Machinery Research Institute)
Some expressway tunnels in Japan have suffered from heaving of the invert or roadbed after several decades in service. It is thought that these heaving are caused by increases in the volume of rock surrounding the tunnel, as occurs when rocks containing clay come into contact with water. Initially, when the amount of heaving is small, road performance can be maintained by cutting or overlay. However, as the heaving increases, cutting and overlay are no longer effective. In such cases, countermeasures include rockbolts and micropiles and, eventually, invert works. The invert works require digging under the road and closing entire lanes of the roadway, which results in social and economic losses.
We developed a new invert structure and an associated construction method as an alternative to the ordinary invert structure. The proposed invert structure, which we call the hybrid invert structure, comprises concrete-filled steel pipes and concrete abutments. Construction of the hybrid invert structure does not require lane closures. The purpose of this study is to identify the optimal structure and construction process for the proposed invert structure based on two-dimensional and three-dimensional finite element analysis.
The results indicate that 1) the optimal invert geometry is an inverted arch-shaped concrete abutment, 2) the optimal steel pipe shape is linear, and 3) the most suitable construction procedure is as follows: the foot of the tunnel lining is excavated and filled with concrete, a relatively short longitudinal section under the lane of each side is excavated before steel pipes are situated, and a series of steel pipes are situated before the excavated area is filled with concrete. The procedure is repeated until the entire length is completed.